1. Field of the Invention
The present invention relates to an EL (Electro-luminescence) display device formed by fabricating a semiconductor device (a device utilizing a semiconductor thin film; typically a thin film transistor) on a substrate, and an electronic device having such an EL display device as a display portion.
2. Description of the Related Art
A technique for forming a thin film transistor (hereinafter referred to as the TFT) on a substrate has been significantly improved in these days, and development for application thereof to an active matrix type display device has continued. In particular, a TFT utilizing a polysilicon film has a field effect mobility higher than that obtainable in a TFT utilizing a conventional amorphous silicon film, thereby realizing an operation at higher speed. Thus, it becomes possible to control pixels by a driving circuit formed on the identical substrate on which the pixels are formed, which is different from the conventional case in which the pixels are controlled by a driving circuit formed in the outside of the substrate.
Such an active matrix type display device has drawn much attention thereto since the device can realize various advantages, such as reduction in manufacturing cost, down-sizing of a display device, an improved yield, a reduced throughput or the like, by fabricating various circuits and devices on one and the same substrate.
In an active matrix EL display device, each pixel is provided with a switching device made of a TFT, and a driving device for controlling a current is activated by the switching device to cause an EL layer (more strictly speaking, a light emitting layer) to emit light. The EL display device is disclosed, for example, in Japanese Laid-open Patent Publication No. Hei 10-189252.
Thus, the present invention is intended to provide an inexpensive EL display device capable of displaying an image with high definition. Furthermore, the present invention is also intended to provide an electronic device having a high recognizability of a display portion by utilizing such an EL display device as the display portion.